Fiber reinforced thermoplastic resin structure, process for production of same, and extruder for production of same

ABSTRACT

A fiber reinforced thermoplastic resin structure comprising a thermoplastic resin and reinforcing fibers, having a ratio (Lw/Ln) of the number average fiber length (Ln) to the weight average fiber length (Lw) of the uniformly dispersed reinforcing fibers of 1.1 to 5, and having a weight average fiber length of 1.0 mm to 200 mm.

This application is a divisional of application Ser. No. 08/277,477,filed Jul. 19, 1994, now U.S. Pat. No. 5,679,456.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fiber reinforced thermoplastic resinstructure controlled in the degree of combing of the reinforcing fibersand fiber length and superior in shapeability (or moldability),mechanical properties, and surface smoothness, a process for productionof the same having a high productivity, and an apparatus for productionof the same. More particularly, it relates to fiber reinforcedthermoplastic resin pellets suitable for making automobile cylinder headcovers, bumper beams, seat frames, instrument panels, wheel caps,battery trays, etc., office automation equipment and home appliancechassis, housings, etc., and further tool housings and fiber reinforcedthermoplastic sheets suited for extrudates, blow molded products, tubes,pipes, and sheets, and further hot molding use sheets.

2. Description of the Related Art

Fiber reinforced thermoplastic resin structures are used for varioustypes of applications, such as auto parts and parts for officeautomation equipment, making use of their superior mechanicalproperties. In particular, studies are underway for increasing thelength of the reinforcing fibers so as to improve the mechanicalproperties etc. For example, in the case of fiber reinforcedthermoplastic pellets, as shown in Japanese Examined Patent Publication(Kokoku) No. 41-20738, in a method for extruding a chopped strand usingan extruder, the reinforcing fibers end up breaking and therefore goodmechanical properties cannot be exhibited. Accordingly, studies havebeen pursued so as to increase the fiber length of the reinforcingfibers so as to improve the mechanical properties etc. As shown inJapanese Examined Patent Publication (Kokoku) No. 63-37694, a roving ofreinforcing fiber connected by the pultrusion method is covered with aplastic and cut into predetermined lengths to form pellets. Further,there are also known pellets with uniformly dispersed reinforcing fibersof a fiber length of 3 to 20 mm obtained by the paper machine processand the dry nonwoven fabric process as shown in Japanese UnexaminedPatent Publication (Kokai) No. 3-7307 and pellets obtained by mixing aresin powder and glass fibers in advance in a Henschel mixer etc. andthen melting in a ram extruder as shown in Japanese Unexamined PatentPublication (Kokai) No. 63-9511. Further, in the case of thermoformablesheets, there are known sheets obtained by the laminate method ofsandwiching in a glass fiber mat between thermoplastic resin sheets suchas shown in Japanese Examined Patent Publication (Kokoku) No. 63-15135,sheets obtained by the paper making machine process includingdiscontinuous filaments of 7 to 50 mm length such as shown in JapaneseExamined Patent Publication (Kokoku) No. 4-40372, the process forobtaining thermoplastic resin sheets by mixing thermoplastic resinpowder and reinforcing fibers under a jet of air, causing the mixture toaccumulate on a conveyor belt to transport the same and at the same timeheating and pressurizing the same to melt the thermoplastic resin suchas shown in Japanese Unexamined Patent Publication (Kokai) No. 59-49929and Japanese Unexamined Patent Publication (Kokai) No. 62-208914, and athermoplastic resin sheet obtained by the method of introducingthermoplastic resin and a web-like material of glass fibers of 3 to 100mm length into an extruder and feeding the same into a melt extrusiondie to form a web sheet such as shown in Japanese Unexamined PatentPublication (Kokai) No. 2-235613.

Further, as the method for feeding a continuous roving into an extruder,there is known the method of placing the glass fibers into the melt in ascrew extruder in the form of a braid and cutting it into suitablelengths such as shown in Japanese Examined Patent Publication (Kokoku)No. 44-16793. Further, as attempts to control the degree of combing andfiber length of reinforcing fibers by an extruder, there are known theprocess of supplying a glass roving from the second supply port of atwin-screw extruder to separate it into filaments such as in JapaneseUnexamined Patent Publication (Kokai) No. 58-56818, a reinforcedmaterial such as shown in Japanese Unexamined Patent Publication (Kokai)No. 60-221460, a material dispersed with short fibers cut in thekneading apparatus such as shown in Japanese Unexamined PatentPublication (Kokai) No. 4-125110, and the process of kneading usingpiston motion such as shown in Japanese Examined Patent Publication(Kokoku) No. 4-80810. Further, as an extruder with a processed screw orcylinder, there are known screws provided with combing and kneadingregions having large numbers of projections for grinding down organicfillers such as shown in Japanese Examined Patent Publication (Kokoku)No. 62-57491, screws of barrier type mixing sections roughened to crushthe inorganic matter, additives, etc. such as shown in Japanese ExaminedPatent Publication (Kokoku) No. 63-56845, and kneading elements composedof specially processed cylinders or screws for kneading thermoplasticresins such as shown in Japanese Examined Patent Publication (Kokoku)No. 60-8934.

However, in the above structures, while the reinforcing fibers becomelonger in length, their degree of combing and kneading action areinsufficient, and therefore, not only are the fluidity and mechanicalproperties insufficient, but also the productivity thereof is low. Inparticular, pellets obtained by the pultrusion process and pelletsobtained by the process of Japanese Examined Patent Publication (Kokoku)No. 44-16793 contain fibers of long fiber length, but the degree ofcombing of the fibers is also poor, so when press formed, the plasticand fibers end up separating or the fluidity at the time of injectionmolding is poor. Further, in the case of the paper-machine process,while there is no fiber breakage and uniform shaped articles with fibersdispersed down to the filament level are obtained, the kneading actionis small, so the bonding strength at the interface of the plastic andreinforcing fibers is low and the mechanical properties are inferior.Further, the glass mat laminate process gives superior mechanicalproperties, but the fluidity is poor at the time of press forming andother hot molding and the fiber does not flow to the corner portionsetc. Therefore, there has been a demand for a fiber reinforcedthermoplastic resin structure controlled in degree of combing and fiberlength of the reinforcing fibers, superior in fluidity, mechanicalproperties, and surface smoothness, and high in productivity.

In general, use of an extruder enables a high productivity, but in theprocesses of Japanese Unexamined Patent Publication (Kokai) No.58-56818, Japanese Unexamined Patent Publication (Kokai) No. 60-221460,Japanese Unexamined Patent Publication (Kokai) No. 41-25110, andJapanese Examined Patent Publication (Kokoku) No. 4-80810, the degree ofcombing and fiber length of the reinforcing fibers could not besufficiently controlled and when the kneading action of the screw wasstrengthened, the fiber length ended up becoming shorter and themechanical properties falling. If the kneading was made weaker, thedegree of combing became insufficient and the reinforcing fibersnonhomogeneous. Further, Japanese Examined Patent Publication (Kokoku)No. 62-57491, Japanese Examined Patent Publication (Kokoku) No.63-56845, and Japanese Examined Patent Publication (Kokoku) No. 60-8934merely ground down the inorganic or organic fillers and kneaded thethermoplastic resins, so could not control the degree of combing andfiber length of the reinforcing fibers.

SUMMARY OF THE INVENTION

Accordingly, the object of the present invention is to provide a fiberreinforced thermoplastic resin structure which is superior in fluidity,mechanical properties, surface smoothness by dispersing the reinforcingfibers uniformly in the thermoplastic resin to achieve a specificdistribution of fiber lengths while keeping the weight average fiberlength long.

Another object of the present invention is to provide a fiber reinforcedthermoplastic resin structure which is superior in fluidity, mechanicalproperties, surface smoothness, etc. by providing a fiber reinforcedthermoplastic resin structure which is controlled in its degree ofcombing and has reinforcing fibers uniformly dispersed throughout it andwhich is given a specific distribution of fiber length by a kneadingaction while maintaining the weight average fiber length long.

A further object of the present invention is to provide a fiberreinforced thermoplastic resin structure which is superior in fluidity,mechanical properties, surface smoothness, etc. by providing a fiberreinforced thermoplastic resin structure of sheets or pellets which arecombed to a high degree, have a long weight average fiber length, andhave a specific distribution of fiber length.

A further object of the present invention is to provide a process forproduction of a fiber reinforced thermoplastic resin structure superiorin fluidity and mechanical properties by controlling the degree ofcombing and/or fiber length of the reinforcing fibers by melt extrusionof the thermoplastic resin and continuous roving by an extruder having aspecific construction.

A still further object of the present invention is to provide anextruder capable of providing a fiber reinforced thermoplastic resinstructure superior in fluidity and mechanical properties by controllingthe degree of combing, weight average fiber length, or fiber length ofsupplied continuous fibers.

That is, to achieve the objects of the present invention, there isprovided a fiber reinforced plastic structure including reinforcingfibers, which fiber reinforced plastic structure is characterized inthat the ratio (Lw/Ln) of the number average fiber length (Ln) to theweight average fiber length (Lw) of the reinforcing fibers uniformlydispersed in the structure is from 1.1 to 5 and the weight average fiberlength is from 1.0 mm to 200 mm.

Further, the present invention provides a process for production of afiber reinforced thermoplastic resin structure by melt extrusion of thethermoplastic resin and continuous roving by an extruder, which processfor production of a fiber reinforced thermoplastic resin structure ischaracterized in that the degree of combing and/or fiber length of thereinforcing fibers in the plastic matrix are controlled, by the combingaction of irregularly shaped processed surfaces by passing the meltedthermoplastic resin and reinforcing fibers through a control mechanismformed by processing of a screw and/or cylinder to make its surfaceirregular at least at part of the screw surface and/or cylinder innerwall and provides an extruder for production of a fiber reinforcedthermoplastic resin structure provided with a screw and cylinder, whichextruder for production of a fiber reinforced thermoplastic resinstructure is provided with a control mechanism formed by processing ascrew and/or cylinder to have irregularly shaped processed surfacesenabling control of the degree of combing and fiber length by combingthe supplied continuous roving.

Further, there is provided one of the above-mentioned extruderscharacterized by correcting the spiral flow caused by the extruder screwby attaching one or more plates in the cylinder of the extruder betweenthe front end of the screw and the die. When the fiber reinforcedthermoplastic resin structure is a pellet, to prevent breakage of thereinforcing fibers at the die portion during stranding during productionof the fiber reinforced thermoplastic resin pellets, provision is madeof a die assembly which is attached to the front end of the extruderdirectly or via an adaptor and which is thermoplastic resin plates of apredetermined thickness formed with a plurality of through holes, whichdie has through holes of a frustoconical shape, which has a value of R/rgreater than 1 when the radius of the circle formed by a through hole atthe extruder side and the discharge section side are R and r,respectively, which circles formed by the through holes at the extruderside covering at least 90% of the front end of the extruder to which thedie is provided or the discharge sectional area of the adaptor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of the relationship between the winding speed of theglass roving and the rotational speed of the screw in the case of use ofa twin-screw extruder with a screw diameter of 30 mm and polyethyleneterephthalate. The broken line shows the circumferential speed of theoutermost screw flight, while the solid line shows the winding speed ofthe roving. FIG. 2a is a perspective view of a screw processed to have aplurality of blade edges according to a preferable embodiment of thepresent invention, and FIG. 2b is a cutaway perspective view of acylinder processed to have a plurality of blade edges according to apreferable embodiment of the present invention. FIG. 2c is a perspectiveview of a screw processed to have a mesh surface according to apreferable embodiment of the present invention, and FIG. 2d is a cutawayperspective view of a cylinder processed to have a mesh surfaceaccording to a preferable embodiment of the present invention.

FIG. 3 is a schematic sectional view of the screw or cylinder given theplurality of blade edges shown in FIGS. 2a and 2b showing in an enlargedstate the blade edges.

FIGS. 4a, 4c, 4e, and 4g are side views of screws processed according topreferable embodiments of the present invention, and FIGS. 4b, 4d, 4f,and 4h are cutaway perspective views of cylinders processed according topreferable embodiments of the present invention.

FIG. 5a is a sectional view of the state of attachment of plates ofwedge shapes to the inside of the cylinder in front of the screw in atwin-screw extruder as seen from above the extruder. FIG. 5b is asectional view of FIG. 5a seen from the lateral direction of theextruder.

FIG. 6a is a sectional view of the state of attachment of plates ofshapes of two joined wedges to an adaptor portion. FIG. 6b is asectional view of FIG. 6a seen from the lateral direction of theextruder.

FIG. 7a is a sectional view of the state of attachment of plates of acurved shape to the inside of the cylinder in front of the screw in atwin-screw extruder as seen from above the extruder. FIG. 7b is asectional view of FIG. 7a seen from the lateral direction of theextruder.

FIG. 8a is a sectional view of the state of attachment of a plurality ofplates in a lattice to the inside of the cylinder in front of the screwin a twin-screw extruder as seen from above the extruder. FIG. 8b is asectional view of FIG. 8a seen from the lateral direction of theextruder.

FIG. 9 is a sectional view of an extruder cylinder barrel 28 showingfrom the upstream side the section of the downstream side between thefront end of the screw 29 and the plate 25 in FIG. 8.

FIG. 10a is a sectional view of the state of attachment of a dieassembly of the present invention to a twin-screw extruder through anadaptor as seen from above the extruder. FIG. 10b is a sectional view ofthe state of attachment of the die of the present invention to thetwin-screw extruder through the adaptor as seen from the lateraldirection of the extruder.

FIG. 11a is a view of the adaptor in FIG. 10a seen from the extruderside, FIG. 11b is a view of the adaptor seen from the die side, FIG. 11cis a view of the die in FIG. 10a seen from the adaptor side, and FIG.11d is a view of the die seen from the discharge side.

FIG. 12a is a view of a die of a preferable embodiment of the inventionseen from the extruder side,

FIG. 12b is a sectional view of the same seen from the side, and FIG.12c is a view of the same seen from the discharge side.

FIG. 13a is a view of a die of a preferable embodiment of the inventionseen from the extruder side, FIG. 13bis a sectional view of the sameseen from the side, and FIG. 13c is a view of the same seen from thedischarge side.

FIG. 14a is a view of a die of a preferable embodiment of the inventionseen from the extruder side, FIG. 14b is a sectional view of the sameseen from the side, and FIG. 14c is a view of the same seen from thedischarge side.

FIG. 15a is a view of a die of a preferable embodiment of the inventionseen from the extruder side, FIG. 15b is a sectional view of the sameseen from the side, FIG. 15c is a view of the same seen from thedischarge side, and FIG. 15d is an enlarged perspective view of a wedgeshaped partition plate 35.

FIG. 16a is a view of a die of a preferable embodiment of the inventionseen from the extruder side, FIG. 16b is a sectional view of the sameseen from the side, FIG. 16c is a view of the same seen from thedischarge side, and FIG. 16d is a sectional view along A-B in FIG. 16a.

FIG. 17a is a view of a die used in a Comparative Example seen from theextruder side, FIG. 17b is a sectional view of the same seen from theside, and FIG. 17c is a view of the same seen from the discharge side.

FIG. 18 is an overall sectional view of an extruder provided with twosupply ports which is preferably used in the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described in detail below.

The thermoplastic resins usable in the present invention are notparticularly limited in so far as they are thermoplastic which can beshaped or molded by an extruder. Mention may be made for example of apolyethylene, polypropylene, polyvinyl chloride, polyvinylidenechloride, polystyrene, styrene-butadiene-acrylonitrile copolymer, nylon11, nylon 12, nylon 6, nylon 66, and other aliphatic nylons, copolymersof aliphatic nylons further copolymerized with terephthalic acid orother aromatic dicarboxylic acids or aromatic diamines, and otheraromatic polyamides, various copolymerized polyamides, polycarbonate,polyacetal, polymethylmethacrylate, polysulfone, polyphenylene oxide,polybutylene terephthalate, polyethylene terephthalate, polycyclohexanediethylene terephthalate, polybutylene naphthalate, and other polyestersand copolymers of the same, copolymerized polyesters of these polyestersused as hard segments and polytetramethylene glycol or other polyestersor polycaprolactone and other polyesters used as soft segments,thermotropic liquid crystal polymers as described in Japanese ExaminedPatent Publication (Kokoku) No. 3-72099, polyphenylene sulfide,polyether ether ketones, polyether sulfones, polyether imides, polyamideimides, polyimides, polyurethane, polyether amides, and polyesteramides. These may be used alone or in any combinations thereof.

The most preferred plastics are polyethylene, polypropylene,polybutylene terephthalate, polyethylene terephthalate, polycyclohexanedimethylene terephthalate, polyethylene terephthalate copolymer liquidcrystal polymers, nylon 11, nylon 12, nylon 6, nylon 66, aromaticnylons, copolymerized nylons, polyphenylene sulfide, and ABS resin.

As the continuous roving used in the present invention, use ispreferably made of roving comprising a bundle of continuous filaments.The reinforcing fibers are not particularly limited in so far as theynormally can be used for reinforced thermoplastic resins. Use may bemade of glass fiber, carbon fiber, metal fiber, and organic fiber(nylon, polyester, aromatic polyamides, polyphenylene sulfide, liquidcrystal polymers, acrylic, etc.) etc., which may be used alone or in anycombinations thereof. Glass fiber or carbon fiber are most preferred.Further, the fiber diameter is not particularly limited in so far as itis one usually used for reinforcing plastics, but use may preferably bemade of a fiber of a diameter of 1 to 20 μm. In particular, the effectof improvement of mechanical properties is great with a fine fiber of 1to 9 μm or so. The number of filaments bundled in the fiber is notparticularly limited either, but a bundle of 10 to 20,000 filaments ormonofilaments is preferable in terms of handling. Usually, rovings ofthese reinforcing fibers may be used after surface treatment by silanecoupling agent etc. for improvement of the interfacial bonding with thethermoplastic resin. For example, in the case of a polyester resin,surface treatment may be performed by a thermoplastic film formingpolymer, coupling agent, fiber lubricant, etc. known in JapaneseExamined Patent Publication (Kokoku) No. 4-47697 etc. Such surfacetreatment may be performed in advance and use made of the treatedreinforcing fibers or may be performed just before the reinforcingfibers are fed into the extruder so as to continuously produce thestructure of the present invention. The ratio between the thermoplasticresin and fiber is not particularly limited. It is possible to producethe fiber reinforced thermoplastic resin composition and shaped articlesof the same using any ratio of composition in accordance with the finalobject of use, but preferably the content of fibers is 0.5 to 90% byweight, particularly preferably 1 to 60% by weight, in view of themechanical properties and the surface smoothness.

The "structure" of the present invention means blow molded articles, rod(including tubes, pipes, or other hollow articles) or sheet shapedstructures, hot molding use sheets or other fiber reinforcedthermoplastic resin structures, fiber reinforced thermoplastic resinpellets capable of using for injection molding, extrusion, and othertypes of molding of automobile cylinder head covers etc., and injectionmolded articles made by application of the process of production of thepresent invention.

The ratio (Lw/Ln) of the number average fiber length (Ln) to the weightaverage fiber length (Lw) of the reinforcing fibers dispersed uniformlythrough the structure is from 1.1 to 5, more preferably from 1.1 to 3.When this ratio is less than 1.1, the kneading action is small and thebonding at the interface of the thermoplastic resin and fibers isinsufficient, so good mechanical properties and fluidity cannot beobtained. The ratio Lw/Ln has more preferable ranges depending on thetype of the structure. When the structure is a sheet, the ratio is 1.3to 5.0, preferably 1.5 to 4.0, more preferably 1.8 to 3.5. When thestructure is a pellet, the ratio is 1.2 to 3.5, preferably 1.3 to 2.5,more preferably 1.3 to 2.1.

The weight average fiber length of the fibers in the structure is from1.0 mm to 200 mm, preferably 1.0 mm to 15 mm, more preferably 4.5 mm to12 mm. When the weight average fiber length is less than 1.0 mm, theeffect of improvement of the mechanical properties is not obtained.

There are more preferable ranges depending on the type of the structurefor the weight average fiber length as well. When the structure is asheet, the weight average fiber length is from 3 mm to 200 mm,preferably 4 mm to 50 mm. When the structure is a pellet, the weightaverage fiber length is 1.0 mm to 15 mm, more preferably 2.0 mm to 5.0mm.

Further, the "uniform dispersion" of the present invention means thestate where the reinforcing fibers and thermoplastic resin do notseparate when the structure is melted and compressed. It includes astate where the fibers are dispersed to the filament level to a statewhere they are dispersed to the level of bundles of several tens offibers, preferably about five fibers. Further, the "degree of combing"of the present invention can be evaluated by observing a section of thestructure by a microscope and determining the ratio of the number ofreinforcing fibers in bundles of 10 or more in all of 1000 or moreobservable reinforcing fibers (total number of reinforcing fibers inbundles of 10 or more/total number of reinforcing fibers×100) (%). Thisvalue is preferably not more than 60%, preferably 35% or less, andfurther preferably 30% or less. When the structure is a pellet, thesection of the pellets is observed by a microscope and determination ismade of the ratio of the number of reinforcing fibers in bundles of 10or more in all 1000 or more observable reinforcing fibers (total numberof reinforcing fibers in bundles of 10 or more/total number ofreinforcing fibers ×100) (%). This value is preferably not more than 60%and preferably is 35% or less.

The weight average fiber length and the number average fiber length inthe present invention are found by burning off just the thermoplasticresin of a part of a shaped article in a 500° C. electric furnace,photographing the result by a microscope, measuring the lengths of over1000 fibers from the photograph, and determining the values from thedistribution of the fiber lengths.

As the fiber reinforced thermoplastic resin sheet of the presentinvention, mention may be made of fiber reinforced plastic sheets etc.used in various applications and obtained by stamping, compressionmolding, vacuum molding, and other molding methods. The reinforcingfibers are oriented substantially randomly in the plane of the sheet,but depending on the conditions, the ratio of those oriented in thedirection of fluid motion may be higher. As a rod-shaped structure,mention may be made of round rods of a diameter of about 1 to 8 mm, rodswith various other sectional shapes, such as rectangular shapes, hollowrod-shaped articles, etc.

The fiber reinforced thermoplastic resin pellets of the presentinvention are structures obtained by pelletizing the above-mentionedsheets, rods, or other structures by pelletizers or sheet cutters. Whenthe above-mentioned sheets are pelletized, they are cut longitudinallyand laterally, but rod-shaped structures may be cut in just a singledirection and there is less fiber breakage, so it is preferable topelletize rod shaped structures. The pellet length of the pellets ispreferably from 2 mm to 50 mm. Further, to increase the fiber length inthe pellets, the pellet length is preferably at least 1/2 of the weightaverage fiber length of the fiber reinforced plastic structure beforecutting, particularly preferably not more than 15 mm. Further, a featureof the pellets of the present invention is the fact that the weightaverage fiber length in the pellets is shorter than the fiber length ofthe rod-shaped articles etc. and is not more than 0.9 times, sometimesnot more than 0.7 times of the usual pellet length.

Further, the pellets of the present invention can be used forcompression molding, injection molding, extrusion, and other knownmolding methods. Except for compression molding, with the screw moldingmachines usually used for injection molding and extrusion, the fiberlength and the distribution of the reinforcing fibers feeds due to themolding, so in the pellets of the present invention, the fiber lengthand distribution in the pellets is defined, not the fiber length anddistribution of the shaped articles after the injection molding orextrusion.

The process for production of the structure of the present invention isnot particularly limited in so far as the requirements defined by thepresent invention are satisfied, but a preferable process is to producethe fiber reinforced plastic structure by melt extruding a plastic andcontinuous roving in the cylinder of an extruder. More specifically, inthe process, the reinforcing fibers are combed and the fiber lengthcontrolled in the thermoplastic resin matrix by the combing action ofirregularly shaped surfaces by passing the molten thermoplastic resinand continuous roving through a control mechanism formed with a screwand/or cylinder which is processed to make its surface irregular atleast at part of the screw surface and/or cylinder inner wall.

The "extruder with a screw and/or cylinder processed for combing thecontinuous roving and controlling the fiber length" means a single-screwor multi-screw extruder provided inside it with a control mechanism forthe degree of combing and fiber length of the continuous roving. Thecontinuous roving is wound at a fixed speed in the extruder cylinder bythe shearing force between the screw flights and cylinder and advanceswhile being wound on the screw. Usually, the thermoplastic resin flowsthrough the screw grooves, but in the above-mentioned process, thereinforcing fibers advance by riding over the screw flights. Looking ata cross-section of the screw, the flight portion constitutes one part ofthe overall circumference, so the winding speed and the outermostperipheral speed of the screw have a certain deviation from each otheras shown in FIG. 1. FIG. 1 is a graph of the relationship between thewinding speed of the glass roving and the rotational speed of the screwin the case of use of a twin-screw extruder with a screw diameter of 30mm and polyethylene terephthalate. Therefore, by applying variousprocessing to the screw outer circumference and the cylinder inner wall,it is possible to apply a "comb" action between the screw and cylinderto the reinforcing fibers wound on the screw.

As a specific example of a control mechanism, mention may be made ofprocessing on a screw surface or screw flight, preferably a columnarscrew surface or neutral element or other elliptic cylindrical screwsurface, to roughen the same or a cylinder inner wall to roughen thesame. The method of forming the roughness is not particularly limited,but use may be made of cutting, grinding, milling, etc. Further, thetype of roughness includes comb types comprised of grooves andprotrusions, types with grooves and projections formed at specificangles, and meshes formed with grooves longitudinally and laterally. Thefront tips of the projections preferably are made sharp in angle, i.e.,are given a blade-like shape.

FIGS. 2a to 2d and FIGS. 4a to 4h show specific forms of the roughness.The present invention is not limited to these Examples and includes allprocessing functioning as a "comb" combing the reinforcing fibers intofilaments in accordance with the targeted fiber length.

FIG. 2a is an example of an elliptic cylindrical neutral element havingon the screw surface of the element blade-shaped processed portions 2forming roughness with a specific edge angle in the directionperpendicular to the screw shaft. FIG. 2b is an example of a cylinder 3having a blade-shaped processed portion 4 at the inner wall of thecylinder. The blade-shaped processed portions 2 and 4, as shown in FIG.3, can be expressed by the specific edge angle (θ), the height (h) ofthe peaks and valleys of the rough shape, and the distance and pitch (t)between one peak and its adjoining peak.

FIG. 2c is an example of a screw 5 of a neutral element having amesh-like processed portion 6 on the screw surface. FIG. 2d is anexample of a cylinder 7 having a mesh-like processed portion 8 at theinner wall of the cylinder.

FIG. 4a is an example of a full flight screw 9 having a mesh-likeprocessed portion 10 on the flight surface, while FIG. 4b is an exampleof a cylinder 10 having a mesh-like processed portion 12 at the cylinderinner wall. FIG. 4c is an example of a full flight screw 13 having ablade-shaped processed portion 14 on the flight surface, while FIG. 4dis an example of a cylinder 15 having a blade-shaped processed portion16 at the cylinder inner wall. FIG. 4e is an example of a full flightscrew 17 having a blade-shaped processed portion 18 on the flightsurface, while FIG. 4f is an example of a cylinder 19 having ablade-shaped processed portion 20 at the cylinder inner wall. FIG. 4g isan example of a screw 21 of a neutral element having a projection shapedprocessed portion 22, while FIG. 4h is an example of a cylinder 23having a projection shaped processed portion 24. In forming theprojections, it is convenient to use the surface roughness Rz (10 pointaverage roughness of JIS (i.e., Japanese Industrial Standards)standard).

When the fiber length of the reinforcing fibers is long and desiring tocomb to filaments, it is preferable to provide columnar or neutralelement or other elliptic cylindrical elements without flights at partof the screw and to provide parallel blade-shaped projections in thecircumferential direction. The pitch should be made small. For example,the screw 1 shown in FIG. 2a and the screw 21 shown in FIG. 4g arepreferable. Taking as an example the screw 1, the specific edge angle(θ) is preferably not more than 60 degrees, particularly preferably notmore than 45 degrees. The height (h) of the peaks and valleys of therough shape is preferably at least 30 times, preferably at least 75times of the fiber diameter. The pitch (t), that is, the distancebetween one edge and an adjoining edge, is preferably from 30 to 200times of the diameter of the reinforcing fibers.

Further, when desiring that the fiber length be relatively short and thebundled fibers be left relatively numerous within the range satisfyingthe definition of the structure of the present invention, the pitch (t)may be made large or random projections or grooves such as shown in FIG.4e may be provided in the circumferential direction. Alternatively, thescrew 5 or cylinder 7 etc. having the mesh-like processed portions 6 and8 formed with roughness in the longitudinal and lateral directions asshown in FIGS. 2c and 2d are preferable. By using such processed screwsor cylinders, a structure with relatively short fiber lengths andrelatively numerous bundled fibers is obtained.

FIGS. 2a to 2d and FIGS. 4a to 4h illustrated cases of an ellipticalscrew cross-section, but a circular shape is also possible. In the caseof an intermeshing twin-screw extruder, an elliptical shape ispreferable to maintain the self-cleaning action. Further, use may bemade of a combination of different types of processing. Further, tocontrol the fiber length, it is possible to change the length of thecontrol mechanism, change the diameters at the two ends in accordancewith need, or combine projections with different pitches and depths. Thepreferable length of the control mechanism is 0.1 to 10 times, morepreferably 0.2 to 5 times the screw diameter.

In the present invention, it is important to provide a control mechanismcomprised of a columnar or elliptic cylindrical or other screw and/orcylinder roughened on at least part of their surface and inner wall,respectively, at the areas after the charging of the fiber. The pitchand depth of the roughened portions may be changed depending on thedegree of control desired. Further, it is possible to use a so processedscrew or processed cylinder alone or to use a combination of the same.When used in combination, the peaks and valleys of the projections maybe arranged to intermesh or the peaks may be made to approach eachother.

In this way, it is possible to comb the continuous roving and controlthe fiber length. The above-mentioned control mechanism preferably isprovided adjoining the section for feeding the continuous roving. Whentoo far from the feeding portion, then as described in JapaneseUnexamined Patent Publication (Kokai) No. 61-211367, the reinforcingfibers will fray and break between the usual screw flights and cylinderbefore reaching the control mechanism and control of the fiber lengthand degree of combing will become difficult, and therefore, this is notpreferable. Further, as described in Japanese Unexamined PatentPublication (Kokai) No. 4-125110, when provision is made of a usualkneading portion and backflow portion after the feeding portion, thereinforcing fibers will break there, so this is not preferred either.When a kneading portion is provided between the feeding portion andcontrol mechanism, then in the same way as mentioned earlier, thereinforcing fibers will end up breaking and control will no longer bepossible. Further, even if a kneading portion is provided after thecontrol mechanism, except when particularly desiring to shorten thefiber length, the fiber will end up breaking, so this is not preferredeither.

The charging portion for the continuous roving is provided downstream ofthe melting portion of the plastic, so the roving is fed into the meltedplastic. When fed at the same time as the plastic, then the fibers willbreak at the time of melting of the plastic and control will no longerbe possible, and therefore, this is not preferred.

The extruder usable in the present invention is not particularlylimited, but a multi-screw extruder such as a modular twin-screwextruder is convenient. As a multi-screw extruder, the most generaltwin-screw extruder is preferred, but any type is acceptable, such as aco-rotating, counter-rotating, intermeshing, and non-intermeshing type.Further, the screws may have deep grooves or shallow grooves or besingle flighted, double flighted, triple flighted, etc. A twin-screwextruder, compared with a single-screw extruder, enables independentcontrol of the amount of plastic supplied and the rotational speed ofthe screws, so enables easy control of the amount of addition of thereinforcing fibers. Further, if a modular construction, there is theadvantage of the ease in provision of a control mechanism forcontrolling the degree of combing and fiber length and ease in changingthe position of the same.

From the viewpoint of preventing a deterioration in the physicalproperties and defective appearance due to volatile componentsevaporating from the thermoplastic resin or fiber or air bubbles caughtamong the reinforcing fibers, it is preferable to provide a vent portafter the control mechanism used for controlling the degree of combingand fiber length.

Further, according to the present invention, by correcting the spiralflow, caused by the screw in the mixed melt of the reinforcing fibersand thermoplastic resin controlled in degree of combing and fiber lengthby the control mechanism, by plates provided inside the cylinder betweenthe front end of the screw and the die, the problem of the unstablefluid motion at the time of extrusion of the mixed melt can beeliminated and a fiber reinforced thermoplastic resin structure superiorin surface smoothness, i.e., not having a rough surface of theextrudate, can be obtained.

The plates preferably used in the present invention are for correctingthe spiral flow of the mixed melt extruded by the screw in the extruderand may be of any shape so long as they have that effect, but it ispreferable from the viewpoint of preventing buildup of the reinforcingfibers at the plates that at least part of the plates be wedge shaped,in particular, that the side at the supply of material in the extruderbe wedge shaped.

The angle of the wedge is preferably not more than 90 degrees, morepreferably not more than 60 degrees, in view of preventing buildup ofreinforcing fibers on the plates. Further, the plates may be curved tomore effectively correct the spiral flow. The type of the curving is notparticularly limited, but mention may be made of a plate curved to ashape of an arc, part of an ellipse, parabola, etc. over its entirearea, a plate curved to a shape of an arc, part of an ellipse, parabola,etc. at just the extruder side, a plate curved to a shape of an arc,part of an ellipse, parabola, etc. at just the discharge side, etc. Aplate 25 curved to a shape of part of an ellipse at just the dischargeside, shown in FIGS. 7a and 7b, is preferable in terms of the control ofthe fluid motion of the plastic. The direction of curving is also notparticularly limited, but it is preferable to curve it in the directionof rotation of the screw and in a direction of a high correction effectin accordance with the depth of intermeshing of the screw of theextruder. Further, plates with different directions of curving may becombined in use.

The length of the plates in the screw axial direction is at least 0.2 interms of the L/D of the screw, particularly preferably at least 0.4, inview of the effect of control of the spiral flow.

The material of the plates usable in the present invention is notparticularly limited and use may be made of known materials, but generalsteel or the steel processed for wear resistance used in cylinders,screws, etc. of extruders, are preferable in view of the superiority inwear resistance for the reinforcing fibers. Further, super rigidmaterials are preferable from the viewpoint of the wear resistance forthe reinforcing fibers, in particular, ceramics are preferred.

Regarding the position of mounting of the plates, any position ispossible in the cylinder barrel of the extruder between the front end ofthe screw and the die, but placement at a position at least 0.1,preferably at least 0.3, in terms of the L/D of the screw, from thefront end of the screw is preferable in terms of suppressing the spiralflow caused by the screw. The number of the plates is not particularlylimited, but from the viewpoint of resistance to clogging by thereinforcing fibers, a number is preferred which gives an area occupiedby the plates, in any cross-section perpendicular to the screw axiswhere the plates are placed, of not more than 50% of the barrelcross-section, preferably not more than 30%.

When a plurality of plates are attached, the distance between them maybe equal or irregular, but it is preferable that the distance betweenplates be greater than the average fiber length of the reinforcingfibers in the extrudate comprised of the reinforcing fibers and thethermoplastic resin in view of preventing the clogging between plates bylong reinforcing fibers.

The direction of attachment of the plates is not particularly limited,but the plates may be attached in a direction parallel to the screw axis(angle with screw axis of 0 degree) or inclined from the paralleldirection in a range of 0 to 45 degrees.

Further, to more efficiently correct the spiral flow, a plurality ofplates may be used in numerous stages at different mounting positions ormay be combined in a lattice. As cases of combination in a lattice,mention may be made of a combination of vertical plates and horizontalplates as shown in FIGS. 8 and 9, a combination of vertical platesinclined from the vertical axis in a small range from 90 degrees,preferably a range of 5 to 60 degrees, and horizontal plates, acombination of horizontal plates so inclined and vertical plates, etc.

Typical examples of the plates preferably used in the production of thefiber reinforced thermoplastic resin structure of the present inventionare shown in FIGS. 5 to 8. FIG. 5a is a sectional view of the state ofattachment of plates 25 of the present invention in wedge shapes to theinside of the cylinder barrel 28 in front of the screw 29 in atwin-screw extruder as seen from above the extruder. FIG. 5b is asectional view of FIG. 5a seen from the lateral direction of theextruder. FIG. 6a is a sectional view of the state of attachment ofplates 25 of two joined wedge shapes to an adaptor 27 portion as seenfrom above the extruder, while FIG. 6b is a sectional view of FIG. 6aseen from the lateral direction of the extruder. Here, the adaptor 27 isa device attached between the extruder body and the die 26 for mountingthe die 26. FIG. 7a is a sectional view of the state of attachment ofplates 25 of a curved shape to the inside of the cylinder barrel 28 ofthe extruder in front of the screw 29 in a twin-screw extruder as seenfrom above the extruder. FIG. 7b is a sectional view of FIG. 7a seenfrom the lateral direction of the extruder. FIG. 8a is a sectional viewof the state of attachment of a plurality of plates 25 in a lattice tothe inside of the cylinder barrel 28 in front of the screw 29 in atwin-screw extruder as seen from above the extruder, while FIG. 8b is asectional view of FIG. 8a seen from the lateral direction of theextruder. FIG. 9 is a sectional view of an extruder cylinder barrel 28showing from the upstream side the section of the downstream sidebetween the front end of the screw 29 and the plate 25 in FIG. 8. Theplates 25 are attached to the inside of the extruder cylinder barrel 28or the portion of the adaptor 27 in front of the screw 29 of atwin-screw extruder. The spiral flow of the mixed melt extruded from thescrew 29 is corrected by the plates 25 and the melt is discharged fromthe discharge port 30 of the die 26 attached through the adaptor 27 ordirectly to the extruder.

In the present invention, during the production of the pellet form ofthe fiber reinforced thermoplastic resin structure, to prevent breakageof the reinforcing fibers at the die portion and clogging of the dieholes by the reinforcing fibers when stranding the mixed melt of thereinforcing fibers and thermoplastic resin controlled in degree ofcombing and fiber length, obtained from the control mechanism, by a die,it is possible to use an extrusion die having a die holes having afrustoconical shape and/or land portions having parallel portions of afixed diameter following the same so as to reduce the breakage of thereinforcing fibers at the die and to prevent buildup of the reinforcingfibers at the die portion due to that shape and thereby to strand thefiber reinforced thermoplastic resin more stably without disturbing thefiber length of the mixed melt of the reinforcing fibers andthermoplastic resin controlled in degree of combing and fiber length.

The die preferably used in the present invention has a plurality ofthrough holes. The through holes have frustoconical shapes and have avalue of R/r greater than 1 when the radius of the circle formed by athrough hole at the extruder side and the discharge section side are Rand r, respectively. The circles formed by the through holes at theextruder side cover at least 90% of the front end of the extruder towhich the die is provided or the sectional area of the discharge side ofthe adaptor.

The extruder and the die assembly of the present invention may beconnected by direct attachment of the assembly to the front end of theextruder or attachment through an adaptor. The construction and materialof the adaptor are not particularly limited. Attachment is possible byan adaptor of a known construction and/or material, but a constructionwith no retention portions is preferable in view of preventing cloggingof the die holes. Further, a method which smooths the surface roughnessof the wall of the adaptor along which the plastic flows by the methodas for example disclosed in Japanese Unexamined Patent Publication(Kokai) No. 5-220811 is preferable. It is particularly preferable thatthe average centerline roughness Ra by the replica method be ≦5 μm. As amethod achieving a satisfactory surface roughness when making thethrough holes in the adaptor, electrodischarge machining and reamingafter machining are preferred.

The through holes of the die holes in the present invention arefrustoconical in shape. The value of R/r is greater than 1 when theradius of the circles formed by a through hole at the extruder side andthe discharge section side are R and r, respectively. Further, thecircles formed by the through holes at the extruder side cover at least90% of the front end of the extruder to which the die is provided or thesectional area of discharge side of the adaptor, preferably at least95%. The "cone" of the frustoconical shape referred to in the presentinvention may be a mathematically conical shape or a substantiallyconical shape with a curved side cross-section. In the case of asubstantially conical shape, it is preferable that the curve at the sidecross-section be one which protrudes inward.

Further, in the present invention, a parallel land portion of a fixeddiameter may be provided before a conical through hole of the die. Theland portion is for stabilizing the flow of the mixture of thereinforcing fibers and the plastic and is not particularly limited inlength, but usually when using as a unit the ratio L/D of the diameter Dof the land (which equals the radius r of the die outlet port) and thelength L of the land, an L/D of 1 to 50, particularly 3 to 10, ispreferred.

When the distance d between centers of the circles formed by theadjoining through holes of the die on the extruder side is not more than10 mm, it is possible to further reduce the buildup of the longreinforcing fibers at the partition portion of the two through holes.Further, to prevent buildup of reinforcing fibers at the partitionportion between adjoining die holes, it is preferable that thefrustoconical shapes forming the through holes partially overlap. Theoverlapping portions are preferably left empty or are provided withfurther wedge shaped partition plates to prevent buildup of reinforcingfibers in the through holes.

Further, to prevent buildup of the reinforcing fibers due to retentionportions and damage to the reinforcing fibers due to sudden changes inthe flow path when the mixture of the reinforcing fibers and the plasticflows in the die, it is preferable to use a die in which at least partof the through holes at the extruder side of the die are enlarged insize so that the shape of the front end of the extruder to which the dieis attached or the cross-section at the discharge side of the adaptorand the shape of the holes formed by the through holes at the extruderside of the die match.

Typical examples of the die assemblies used in the production of thepellet form fiber reinforced thermoplastic structure in the presentinvention are shown in FIG. 10 to FIG. 16. FIG. 10a is a sectional viewof the state of attachment of a die assembly of the present invention toa twin-screw extruder through an adaptor 27 as seen from above theextruder. FIG. 10b is a sectional view of the state of attachment of thedie 26 of the present invention to the twin-screw extruder through theadaptor 27 as seen from the lateral direction of the extruder. FIG. 11ais a view of the adaptor 27 in FIG. 10a seen from the extruder side,FIG. 11b is a view of the adaptor 27 seen from the die side, FIG. 11c isa view of the die 26 in FIG. 10a seen from the adaptor side, and FIG.11d is a view of the die 26 seen from the discharge side. The dieassembly is attached through the adaptor 27 by bolts 31 to the extrudercylinder 28 provided with the screw 29. The adaptor 27 has adaptor inletholes 32 at the face seen from the extruder side and adaptor outletholes 33 at the face seen from the discharge side. The adaptor inletholes 32 and the adaptor outlet holes 33 form through holes. The die 26has die inlet holes 37 at the face seen from the adaptor side and dieoutlet holes 30 at the face seen from the discharge side. Through holesare formed by the die inlet holes 34 and the die outlet holes 30. Aplurality of through holes are provided at a center distance d from theadjoining through holes.

FIGS. 12 to 16 are views showing typical constructions of the dies inthe present invention, with A being views seen from the extruder side, Bcross-sectional views seen from the lateral sides, and C views seen fromthe discharge side.

FIGS. 12a to 12c show an example of a die formed with through holeshaving a frustoconical shape by the die inlet holes 34 of the radius Rand the die outlet holes 30 of the radius r, FIGS. 13a to 13c show anexample of a die having funnel shaped through holes comprised of dieinlet holes 34 of the radius R and land portions of the land diameter rand land length L, FIGS. 14a to 14c show a die having funnel shapedthrough holes in which the frustoconical shapes forming the throughholes partially overlap, FIGS. 15a to 15c show an example of the die ofFIGS. 14a to 14c in which wedge shaped partition plates 35 are providedto partition the adjoining through holes at the empty locations formedas a result of the partial overlap of the frustoconical shapes, and FIG.15d is a perspective view of a wedge shaped partition plate 35. FIGS.16a to 16c show an example of the die of FIGS. 13a to 13a in which theinlet holes 34 of the die are enlarged so as to match with the shape ofthe discharge holes of the front end of the extruder or the outlet holesof the adaptor, and FIG. 16d is a sectional view along A-B in FIG. 16a.

The strand-form fiber reinforced plastic structure obtained by theabove-mentioned die assembly may be made into a pellet-form fiberreinforced plastic structure by pelletizing by a known method. Thepelletizing is preferably performed, as shown in for example JapaneseExamined Patent Publication (Kokoku) No. 41-20738, by the method ofcooling the strands and then cutting them into pellets or the method ofcutting the strands to predetermined dimensions immediately afterextrusion from the die. Further, the die assembly of the presentinvention may be used together with the plates for correcting the spiralflow caused by the screw mentioned above.

The fiber reinforced thermoplastic resin pellets of the presentinvention may be used for injection molding, injection press molding,extrusion of tubes, pipes, etc., blow molding, and other known moldingprocesses and are superior in fluidity compared with even theconventional pultrusion method. At the time of molding, it is preferableto make the nozzles and gate shapes larger and to make the depth of thegrooves of the screws of the molding machines greater than the size ofthe pellets so as to keep down damage to the reinforcing fibers.

A feature of the process of production of the present invention is thatalloying of known thermoplastic resin and addition of various additivesare simultaneously possible. The fiber reinforced thermoplastic resinstructure of the present invention may be given desired properties inaccordance with their object of use by mixing in known substancesgenerally used for thermoplastic resin, such as antioxidants, heatresistance stabilizers, ultraviolet absorbants, and other knownstabilizers, antistatic agents, flame retardants, flame retardantadjuvants, dyes, pigments, and other coloring agents, lubricants,plasticizers, crystallization accelerators, crystal nucleating agents,etc. Further, it is possible to simultaneously mix in glass flakes,glass powder, glass beads, silica, montmorillonite, quartz, talc, clay,alumina, carbon flakes, wollastonite, mica, calcium carbonate, metalpowder, and other inorganic fillers.

Next, a specific preferable example of the process for production of thepresent invention will be explained with reference to the drawings. FIG.18 is a cross-sectional view of the entire double flighted screw typetwin-screw extruder preferably used in the present invention. Thethermoplastic resin is fed from the first feed port 39 and is meltedwhile being transported in the extrusion direction by the screw 29. Thethermoplastic resin is completely melted in the kneading zone 41. Afterthis, the fiber in the roving state is fed from the reinforcing fiberfeeding port 40. The molten thermoplastic resin and fiber are sent tothe front end of the screw by the screw comprised of the forward fullflights 42. The fibers are combed and the fiber length controlled by thecontrol mechanism 43 adjoining the charging port 40, then the mix ispassed through the through holes of the adaptor 27 and die 26 to extrudethe fiber reinforced thermoplastic resin structure 46 and thereby obtainthe final fiber reinforced thermoplastic resin structure. Also, it ispossible to form the roughened surface 45 on the cylinder inner wall 38corresponding to the screw roughed surface 43. Further, to correct thespiral flow caused by the screw, it is possible to attach the platesillustrated in FIGS. 5 to 9.

EXAMPLES

The present invention will be explained in further detail below usingExamples, but the invention is not limited to the same. The figures forthe mechanical properties shown in the Examples and Comparative Examplesare mean values of measurements taken from 10 samples.

In evaluating the Izod impact strength, measurement was performed inaccordance with ASTM D-256. The flexural modulus was evaluated bymeasurement in accordance with ASTM D-790. In the case of fiberreinforced thermoplastic resin pellets, test pieces were prepared inaccordance with the above standards by injection molding. At that time,to evaluate the pellet fluidity, the lower limit pressure of moldingduring the injection molding was measured and used as an index. In thecase of a sheet, test pieces were cut out from the sheet and measured.The fibers in structures were observed by placing ten pieces of pelletsor part of a sheet (10 cm square portion at center of sheet or, in thecase of a sheet having a width of less than 10 cm, a rectangle havingsuch a length that the area thereof is 100 cm²) in a 500° C. electricfurnace and burning off just the plastic to measure the fiber content.Further, at least 1000 fibers in the ash were examined by a microscope,the weight average fiber length (Lw) and number average fiber length(Ln) were found from the distribution of fiber lengths, and the ratioLw/Ln was found. Note that the corner portion of the shaped article (1cm square portion at outer circumference of sheet) was similarly burnedto measure the fiber content.

The state of dispersion of the reinforcing fibers was evaluated byfurther melt compressing the pellets or sheet and giving a poor ("X")rating to cases of separation of the reinforcing fiber and plastic and agood ("0") rating to cases of no separation of the reinforcing fibersand thermoplastic resin.

As a simple way of evaluating the degree of combing of the fibers, asoft X-ray photograph was taken of a structure processed to a thicknessof 1 mm. A poor ("X") rating was given to the case where the portion ofuneven concentration exceeded 3 mm square, a fair ("Δ") rating to thecase of a portion of less than 3 mm, and a good ("0") rating to the caseof no uneven portions. Alternatively, the degree of combing was found byexamining under a microscope a cross-section of the structure cut by arazor and determining the ratio of fibers in bundles of 10 or more in1000 fibers.

The relative viscosity of the plastic was measured at 25° C. afterdissolving it in o-chlorophenol at a concentration of 0.5 g/dl.

Example 1 and Comparative Examples 1 to 3

Use was made of a co-rotating twin-screw extruder (TEX30 made by JapanSteel Works Ltd.) having two supply ports in the extrusion direction, ascrew diameter of 30 mm, and an L/D of 45.5 as shown in FIG. 18.Further, use was made of double flighted intermeshing 3.5 mm screws.Between the first plastic feed port 39 and the reinforcing fiber feedingport 40 was provided a screw element 41 comprised of five kneading disksof an L/D of 1 and 45 degree inclination combined in a right-handed andleft-handed order. At the discharge side of the reinforcing fiberfeeding port 40 was provided, via a full-flight screw 42 of an L/D of 1,an elliptical cross-section kneading element with the processing of FIG.2a (pitch (t) of 1 mm, blade angle (θ) of 30 degrees, and height (h) ofpeaks and valleys of 1 mm) and an L/D of 0.75, to form the controlmechanism 43. Polyethylene terephthalate pellets (relative viscosity of1.35) were fed to the plastic feed port 39 by a screw pellet feeder,glass roving of a diameter of 17 μm and a weight of 2200 g per 1000meters (made by Nippon Electric Glass Co.) was introduced from the fiberfeeding port 40, and the mix was extruded in a sheet form from a die ina thickness of 4 mm and a width of 50 mm under conditions of a cylindertemperature of 280° C. and a screw rotational speed of 200 rpm. Thesheets were cooled by a casting roll to obtain the fiber reinforcedsheet. The content of the glass fibers in the obtained sheets was 25% byweight and the glass fibers were uniformly dispersed (Example 1).

For comparison, using the above-mentioned polyethylene terephthalatepowder and chopped strands of a fiber diameter of 17 μm and fiber lengthof 13 mm, the porous web sheets with a glass fiber content of 25% byweight were prepared using a hand sheet making machine from an aqueousslurry of polyethylene terephthalate powder and chopped strands by thesame paper machine process as in Japanese Unexamined Patent Publication(Kokai) No. 3-7307. Five of the web sheets were superposed and pressformed at about 280° C. to obtain sheets (Comparative Example 1). Also,using the same method as in Japanese Unexamined Patent Publication(Kokai) No. 63-9511, the same type of polyethylene terephthalate andglass fiber as in Comparative Example 1 were mixed in a Henschel mixer,then were extruded into sheets by a ram extruder to obtain sheets of aglass fiber content of 25% by weight (Comparative Example 2). Further,using the same type of polyethylene terephthalate and glass roving as inthe example, the known crosshead die pultrusion was performed. Theresults were cut into pellets of a length of 13 mm to obtain long fiberreinforced pellets of a glass content of 25% by weight. The pellets werepress formed into sheets at about 280° C. (Comparative Example 3).

As shown in Table 1, when the fiber length, distribution, and mechanicalproperties of the sheets were measured, with the example of theinvention, it was found that superior mechanical properties could beobtained, but in Comparative Examples 1 and 2, the specifieddistribution of fiber length could not be obtained by melt extrusion, sodespite the long fiber length, only a low impact strength could beobtained. Further, in Comparative Example 3, the glass roving was notcombed, so the plastic and glass fibers separated upon press forming anda uniform sheet could not be obtained, so the mechanical propertiescould not be evaluated.

                  TABLE 1                                                         ______________________________________                                                            Comp.   Comp.   Comp.                                                   Ex. 1 Ex. 1   Ex. 2   Ex. 3                                     ______________________________________                                        Process of production   Paper   Dry   Pultrusion                                                      machine process                                       Fiber content (wt %)                                                                          25      25      25    25                                      Lw (mm)         4.9     13      13    13                                      Lw/Ln           1.7     1.0     1.0   1.0                                     Izod impact strength (J/m)                                                                    220     121     130   --                                      with notches                                                                  Flexural modulus of elasticity                                                                8100    7500    7300  --                                      (MPa)                                                                         State of dispersion of fibers                                                                 ◯                                                                         X       X     X                                       ______________________________________                                    

Examples 2 to 4 and Comparative Examples 4 to 5

The same procedure was followed as in Example 1, except that as thecontrol mechanism 43 of the screw, use was made of a neutral element ofan L/D of 0.75 and an elliptical cross-section given the processing ofFIG. 2a (pitch (t) of 0.5 mm, blade angle (θ) of 60 degrees, and height(h) of 0.4 mm) or of FIG. 4g (projections giving a surface roughness Rzof 90 μm) and a forward full flight element of an L/D of 1 given theblade processing of FIG. 4e (pitch (t) of 1 mm, blade angle (θ) of 30degrees, and height (h) of peaks and valleys of 1 mm) and extrusion wasperformed under conditions of a screw rotational speed of 150 rpm, so asto extrude the melt into sheets. These were cooled by a casting roll toobtain fiber reinforced sheets. For comparison, sheets were formed inthe same way using a forward full flight element (Comparative Example 4)without processing instead of the forward full flight element given theprocessing of Example 4 and a neutral element (Comparative Example 5)without processing instead of the neutral element given the processingof Example 2. As shown in Table 2, in Comparative Examples 4 and 5, thedie pressure was high, uneven discharge was caused, the degree ofcombing of the glass fibers in the sheets was uneven, and thereinforcing fibers and plastic separated when the sheets were melted andcompressed, but in Examples 2 to 4, good sheets were obtained.

                  TABLE 2                                                         ______________________________________                                               Ex. 2 Ex. 3   Ex. 4   Comp. Ex. 4                                                                           Comp. Ex. 5                              ______________________________________                                        Fiber content                                                                          27      27      27    27      27                                     (wt %)                                                                        Control  FIG. 2a FIG. 4g FIG. 4e                                                                             None    None                                   element                        Forward full                                                                          Neutral                                                               flight                                         Lw       5.3     4.6     8.0   24      19                                     Lw/Ln    2.1     2.3     2.6   3.5     3.1                                    Die pressure                                                                           1.1     1.4     1.5   2.1 to 2.5                                                                            1.8                                    (MPa)                                                                         Discharge                                                                              ◯                                                                         ◯                                                                         ◯                                                                       X       Δ                                stability                                                                     State of ◯                                                                         ◯                                                                         ◯                                                                       X       X                                      dispersion of                                                                 fibers                                                                        Degree of                                                                              ◯                                                                         ◯                                                                         ◯                                                                       X       Δ                                combing of                                                                    fibers (simple                                                                evaluation                                                                    method)                                                                       ______________________________________                                    

Example 5 and Comparative Example 6

The same procedure was followed as in Example 1, except that use wasmade of glass roving of a diameter of 13 μm and a weight of 1100 g per1000 meters (made by Nippon Electric Glass Co.) and extrusion wasperformed through a sheet die under conditions of a cylinder temperatureof 290° C. and a screw rotational speed of 200 rpm. The sheets wereextruded at a thickness of 5 mm, a width of 80 mm, and a speed of 80cm/minute, were cooled by a cooling belt, then were cut into lengths of300 mm to obtain fiber reinforced plastic sheets. The obtained sheetswere dried at 130° C. for 6 hours, then were compression molded at apress temperature of 280° C. and were measured for their mechanicalproperties, fiber lengths, etc. The content of glass fiber of the sheetsobtained was 45% by weight (Example 5).

Further, sheets of polyethylene terephthalate the same as in Example 1pressed to a thickness of 1.5 mm and mats of chopped strands of a basisweight of 100 g/m² and a fiber length of 50 mm were superposed to give acontent of glass fibers of 45% by weight, then were press molded atabout 280° C. to obtain a sheet of a thickness of 5 mm, a length of 250mm, and a width of 250 mm (Comparative Example 6). The sheet ofComparative Example 6 was dried, then compression molded in the same wayas in Example 5 and measured for mechanical properties and fiber length.

As shown in Table 3, in the Example of the present invention, it waspossible to obtain fiber reinforced thermoplastic resin sheets superiorin mechanical properties and superior in fluidity of the fibers to thecorner portions as well. In Comparative Example 7, high mechanicalproperties could be obtained, but the degree of combing of the fiberswas poor and the fluidity was poor, with little content of fibers at thecorner portions.

                  TABLE 3                                                         ______________________________________                                                                    Comp.                                                                   Ex. 5 Ex. 6                                             ______________________________________                                        Lw (mm)                 37      49                                            Lw/Ln                   2.5     1.1                                           State of dispersion of fibers                                                                         ◯                                                                         X                                             Degree of combing (%)   20      98                                            1/8" notch Izod (J/m)   200     260                                           Flexural strength (MPa) 240     280                                           Flexural modulus (MPa)  14100   15100                                         Fiber content at corners of shaped article (wt %)                                                     43      5                                             ______________________________________                                         Lw: Weight average fiber length in sheets                                     Ln: Number average fiber length in sheets                                

Examples 6 to 7 and Comparative Examples 7 to 8

The same procedure was followed as in Example 5 except for usingpolybutylene terephthalate (PBT1100S made by Toray Industries) andcarbon fiber ("Torayca" T-300B made by Toray Industries) roving so as toproduce fiber reinforced plastic sheets of a content of fiber of 20% byweight and a sheet thickness of 4 mm. These were extruded at a speed ofabout 100 cm/minute, cooled by a cooling belt, then cut into lengths of300 mm to obtain fiber reinforced plastic sheets (Example 6). Further,the same apparatus, plastic, and reinforcing fibers were used as inExample 8, except for using an elliptical section neutral screw elementof an L/D of 0.75 and given the mesh processing of FIG. 2c (pitch (t) of0.5 mm, blade angle (θ) of 30 degrees, and height (h) of peaks andvalleys of 0.5 mm) instead of the elliptical section neutral elementused as the control mechanism 43 in the extruder of Example 6, so as toobtain fiber reinforced plastic sheets of a sheet thickness of 4 mm inthe same way as Example 6 (Example 7).

Further, the same apparatus, plastic, and reinforcing fibers were usedas in Example 6 except that in the same extruder as in Example 6,instead of the element of the control mechanism 43, a screw elementcomprised of five kneading disks of an L/D of 0.75 and an inclination of45 degrees was provided combined in right-handed and left-handed order,so as to obtain fiber reinforced plastic sheets of a sheet thickness of4 mm in the same way as in Example 6 (Comparative Example 7). Further,the same apparatus, plastic, and reinforcing fibers were used as inExample 6, except that use was made of a forward full flight screwinstead of the element of the control mechanism 43 in the extruder ofExample 6, to obtain fiber reinforced plastic sheets of a sheetthickness of 5 mm (Comparative Example 8).

As shown in Table 4, the fiber reinforced plastic sheets of the examplesof the invention were all superior in fluidity of the fibers at the timeof molding and exhibited high values of mechanical properties. InComparative Example 8, however, the dispersion of the fibers wasnon-uniform and the combing ability was insufficient as well, so thecontent of fiber at the corners was low. Further, in Comparative Example7, the fiber length in the sheets was short and the mechanicalproperties of the shaped article low.

                  TABLE 4                                                         ______________________________________                                                                    Comp.   Comp.                                                  Ex. 6 Ex. 7    Ex. 7   Ex. 8                                     ______________________________________                                        Lw (mm)        8       5        0.3   15                                      Lw/Ln          2.0     1.8      1.3   2.2                                     State of dispersion of fibers                                                                ◯                                                                         ◯                                                                          ◯                                                                       X                                       Degree of combing (%)                                                                        7       5        0     74                                      1/8" notch Izod (J/m)                                                                        53      46       35    51                                      Flexural strength (MPa)                                                                      250     230      200   250                                     Flexural modulus (MPa)                                                                       11300   11600    10800 11700                                   Fiber content at corners of                                                                  19      20       20    10                                      shaped article (wt %)                                                         ______________________________________                                         Lw: Weight average fiber length in sheets                                     Ln: Number average fiber length in sheets                                

Example 8 and Comparative Examples 9 to 12

The same procedure was followed as in Example 1 to produce long fiberreinforced pellets except that the glass fiber content was made 45% byweight, use was made of the die 4 shown in Table 12 instead of a sheetdie, and the mixture was extruded into rods of a diameter of 4 mm, thenpelletized into lengths of about 10 mm. For comparison, use was made ofthe method of using a similar screw arrangement as in Example 8, using adie 6 shown in Table 12 instead of a sheet die, and adding choppedstrands of 10 mm length from the fiber charging port (ComparativeExample 9), the method of using the die 6 shown in Table 12, usingchopped strands of a length of 10 mm, and using a screw elementcomprised of five kneading disks of an L/D of 0.75 and an inclination of45 degrees combined right-handed and left-handed instead of the controlmechanism 43 (Comparative Example 10), and the method of producingpellets by the known pultrusion method (Comparative Example 11).

As shown in Table 5, in the case of Comparative Example 9, the choppedstrands could not wind around the screw, so were not combed, dieclogging occurred, and pelletizing was not possible. Further, inComparative Example 11, when the discharge was raised to 40 kg/h and thestrand takeup speed was increased, the strands broke and thereforestrands could not be obtained (Comparative Example 12). The pellets ofthis Example according to the present invention were able to increasethe strand takeup speed, and therefore, the pellets were able toefficiently produced and the fluidity of the resultant pellets at thetime of molding was good. Despite of the fact that the weight-averagefiber lengths in the pellets were short when compared with the pelletsproduced by a pultrusion method, the mechanical properties of theresultant injection molded articles were comparable to those of pelletsproduced by a pultrusion method. Furthermore, when the pellets were meltcompressed, the pellets of the present Example did not show anyseparation between the reinforcing fiber and the resin, whereas theseparation between the reinforcing fiber and the rein was caused in thecase of the pellets of comparative Example 11 produced by a pultrusionmethod.

                  TABLE 5                                                         ______________________________________                                                     Comp.    Comp.    Comp.  Comp.                                          Ex. 8 Ex. 9    Ex. 10   Ex. 11 Ex. 12                                  ______________________________________                                        Process of                                                                             FIG. 2a FIG. 2a  right/left-                                                                          Pultrusion                                                                           Pultrusion                            production                                                                             element element  handed                                                                        kneading                                                                      disks                                               Type of fiber                                                                          Roving  10 mm    10 mm  Roving Roving                                                 chopped  chopped                                                              strands  strands                                             Fiber content                                                                          45      45       45     45     45                                    (wt %)                                                                        Discharge                                                                              40      40       40     10     40                                    (kg/h)                                                                        State of ∘                                                                         Die      ∘                                                                        ∘                                                                        Strand                                discharge        clogging               breakage                                               x                      x                                     Rod                                                                           Lw (mm)  5.1              0.5                                                 Lw/Ln    2.2              1.6                                                 Pellets                                                                       Lw (mm)  2.9              0.5    10                                           Lw/Ln    2.0              1.7    1.0                                          State of ∘    ∘                                                                        x                                            dispersion of                                                                 fibers                                                                        Lower limit                                                                            2.1              2.0    4.5                                          pressure at                                                                   molding (MPa)                                                                 Gauge                                                                         Izod impact                                                                            182              77     180                                          strength (J/m)                                                                with notches                                                                  Flexural 15500            13500  15300                                        modulus (MPa)                                                                 Flexural 273              255    275                                          strength (MPa)                                                                ______________________________________                                    

Example 9 and Comparative Examples 13 to 14

The same procedure was followed as in Example 8, but feeding nylon 66(CM3001 made by Toray Industries) to the plastic feed port andintroducing glass roving of a diameter of 13 μm and a weight of 1100 gper 1000 meters (made by Nippon Electric Glass Co.) from the fibercharging port. These were extruded in a strand form under conditions ofa cylinder temperature of 290° C. and a screw rotational speed of 200rpm. The strands were cooled in a water bath, then were cut into lengthsof 10 mm to obtain the fiber reinforced plastic pellets. The content ofglass fiber in the obtained pellets was 45% by weight. The fiberreinforced plastic pellets were dried by vacuum dryer at 90° C. for 24hours, then used for injection molding at a cylinder temperature of 290°C. and a die temperature of 80° C.

The same procedure was followed as in Example 9, but a screw elementcomprised of five kneading disks of an L/D of 0.75 and an inclination of45 degrees was provided at the discharge side of the reinforcing fiberfeeding port as well instead of the control mechanism 43. Otherwise thesame apparatus was used as in Example 9. Nylon 66 the same as in Example9 and glass roving the same as in Example 9, but cut into lengths of 3mm to form chopped strand type reinforcing fibers, were used andextruded into strands by the known process for production of fiberreinforced plastic pellets. The strands were cooled in the same way asin Example 9, then cut into lengths of 10 mm to obtain fiber reinforcedplastic pellets of a glass fiber content of 45% by weight. The pelletswere then dried and used for injection molding by the same method as inExample 9 (Comparative Example 13).

Using the same type of nylon 66 and glass roving as in Example 9 and theknown crosshead die pultrusion process, strands were obtained which werethen cut into pellet lengths of 10 mm to obtain long fiber reinforcedpellets of a glass content of 45 percent by weight. In the same way asin Comparative Example 13, the same method was used as in Example 9 todry the same and then perform injection molding (Comparative Example14).

As shown in Table 6, in the example of this invention, fiber reinforcedplastic pellets superior in the balance of mechanical properties andfluidity could be obtained, but in Comparative Example 13, the fiberlength in the pellets was short, so only a low impact strength could beobtained. Further, in Comparative Example 14, while the fiber length inthe pellets was long, the degree of combing was poor, so the fluidity atthe time of injection molding was poor.

                  TABLE 6                                                         ______________________________________                                                                Comp.   Comp.                                                          Ex. 9  Ex. 13  Ex. 14                                        ______________________________________                                        Lw (mm)            2.2      0.5     10                                        Lw/Ln              2.0      1.2     1                                         State of dispersion of fibers                                                                    ∘                                                                          ∘                                                                         x                                         1/8" notch Izod (J/m)                                                                            230      150     250                                       Flexural modulus (MPa)                                                                           12600    12000   13000                                     Lower limit pressure at molding (MPa)                                                            2.2      2.0     3.7                                       ______________________________________                                         Lw: Weight average fiber length in sheets                                     Ln: Number average fiber length in sheets                                

Example 10 and Comparative Example 15

The same method was used as in Example 9, except for using polybutyleneterephthalate (PBT1100S made by Toray Industries) and carbon fiber("Torayca" T-300B made by Toray Industries) roving, to produce fiberreinforced plastic pellets of a fiber content of 20% by weight and apellet length of 5 mm. These were dried at 110° C. for 12 hours, thenused for injection molding at a cylinder temperature of 260° C. and adie temperature of 80° C.

Use was made of the same apparatus, plastic, and reinforcing fibers asin Example 10, except for providing a screw element comprised of fivekneading disks of an L/D of 0.75 and inclination of 45 degrees combinedin right-handed and left-handed order instead of the control mechanismin Example 10, so as produce and use for injection molding fiberreinforced plastic pellets of a pellet length of 5 mm in the same way asin Example 10 (Comparative Example 15).

As shown in Table 7, the fiber reinforced plastic pellets of the exampleof this invention were superior in fluidity at the time of molding andthe shaped article had high mechanical properties, but in the case wherea screw element processed to improve the combing ability was not used,that is, in Comparative Example 15 where use was made of kneading disks,the fiber length in the pellets became shorter and the mechanicalproperties of the shaped article were low.

In each Example, no separation between the reinforcing fiber and theresin occurred, when the pellets were melt compressed, and thereinforcing fibers were uniformly dispersed in the pellets.

                  TABLE 7                                                         ______________________________________                                                                  Comp.                                                                   Ex. 10                                                                              Ex. 15                                              ______________________________________                                        Lw (mm)               2.5     0.4                                             Lw/Ln                 1.5     1.1                                             Degree of combing (%) 15      2                                               1/8" notch Izod (J/m) 60      40                                              Flexural modulus (MPa)                                                                              12100   11000                                           Lower limit pressure during molding (MPa)                                                           2.7     2.2                                             ______________________________________                                         Lw: Weight average fiber length in sheets                                     Ln: Number average fiber length in sheets                                

Example 11

A screw and cylinder of L/D of 1 and given the processing of FIGS. 4eand 4f (depth of grooves (h) and pitch (θ) both 1 mm) at positionsadjoining the discharge port side of the vent port of an injectionmolding machine having a full flight screw were used, polybutyleneterephthalate resin (relative viscosity of 1.45) was fed from a hopper,and the glass roving of Example 1 was fed from a vent port for injectionmolding at about 250° C. Further, a comparison was made with the case ofno processing (Table 8). The Example of the invention showed goodfluidity at the time of molding and no occurrence of defects in theappearance of the shaped article.

                  TABLE 8                                                         ______________________________________                                                              Ex. 11                                                  ______________________________________                                        Fiber content (wt %)    60                                                    Shaped article                                                                Lw (mm)                 2.5                                                   Lw/Ln                   1.6                                                   Lower limit pressure during molding (MPa)                                                             6.3                                                   Gauge                                                                         Appearance of shaped article                                                                          Good                                                  State of dispersion of fibers                                                                         ◯                                         Number of abnormalities in 100 shots                                                                  None                                                  Izod impact strength (J/m)                                                                            180                                                   with notches                                                                  Flexural modulus (MPa)  14100                                                 Flexural strength (MPa) 210                                                   ______________________________________                                    

Example 12 and Comparative Example 17

Blow molding was performed in the same way as with Example 11 except foruse of a full flight screw blow molding machine. Further, a comparisonwas made with the case of use of a full flight screw with no processinginstead of the processed full flight screw in Example 12 (ComparativeExample 17). In the Example of the invention, the Lw in the moltenparison was 4.9 mm, the Lw/Ln was 2.1, the discharge was stable, and anexcellent shaped article could be obtained, but in Comparative Example17, the Lw was 8.9 mm, the Lw/Ln was 3.4%.

Further, the parison did not hang down vertically, but swung to the leftand right, so a large amount of burrs were caused.

A part of the molded article obtained by a blow molding was cut out,followed by melt compressing and the dispersion conditions of thereinforced fibers were evaluated. In the Example according to thepresent invention, no separation between the reinforcing fibers and theresin occurred and the reinforcing fibers were uniformly dispersed inthe blow molded articles. Contrary to this, when a part of the moldedarticle of the Comparative Example was cut out, followed by meltcompressing, the fibers and the resin were separated ahd the reinforcingfiber was not uniformly dispersed in the blow molded article of theComparative Example.

Examples 13 to 16 and Comparative Examples 18 to 20

The same method was used as in Example 8, except for using polybutyleneterephthalate (PBT1100S made by Toray Industries), to produce 5 mm longpellets with different fiber contents. These were used for injectionmolding and the resultant physical properties were measured (Table 9).For comparison, glass roving was fed from the plastic feeding portinstead of the fiber feeding port.

In each Example, no separation between the reinforcing fibers and theresin occurred, even when the pellets produced were melt compressed, andthe reinforcing fibers were uniformly dispersed in the pellets. Althoughthe good physical properties were obtained in the case of the pelletsaccording to the Examples, in the Comparative Examples, the weightaverage fiber lengths of the reinforcing fibers were all less than 1 mmand the good physical properties were not obtained.

                                      TABLE 9                                     __________________________________________________________________________                              Comp.                                                                              Comp.                                                                             Comp.                                              Ex. 13                                                                             Ex. 14                                                                            Ex. 15                                                                             Ex. 16                                                                            Ex. 18                                                                             Ex. 19                                                                            Ex. 20                                     __________________________________________________________________________    Fiber content                                                                         9    25  45   60  9    25  45                                         (wt %)                                                                        Rod                                                                           Lw (mm) 7.3  6.7 5.9  4.9 0.7  0.6 0.4                                        Lw/Ln   1.9  1.8 1.8  1.9 1.5  1.7 1.5                                        Pellet                                                                        Lw (mm) 5.0  4.3 4.0  3.3 0.7  0.6 0.4                                        Lw/Ln   1.7  1.6 1.5  1.6 1.6  1.7 1.6                                        Izod impact                                                                           58   102 160  164 35   68  111                                        strength (J/m)                                                                with notches                                                                  Flexural modulus                                                                      4250 6980                                                                              12500                                                                              15400                                                                             3500 6340                                                                              11300                                      (MPa)                                                                         Flexural strength                                                                     135  194 231  236 117  166 198                                        (MPa)                                                                         Mold shrinkage                                                                        0.49 0.21                                                                              0.10 0.08                                                                              0.73 0.31                                                                              0.19                                       (%)                                                                           __________________________________________________________________________

Examples 17 to 20 and Comparative Example 21

The same method was used as in Example 8, except for using carbon fiber("Torayca" T-300B made by Toray Industries) roving, to produce 3 mm longpellets with different fiber contents. These were used for injectionmolding. For comparison, the fiber was fed from the plastic feeding portas well instead of the fiber feeding port (Table 10).

In each Example, no separation between the reinforcing fibers and theresin occurred, even when the pellets produced were melt compressed, andthe reinforcing fibers were uniformly dispersed in the pellets. Althoughthe good physical properties were obtained in the case of the pelletsaccording to the Examples, in the Comparative Examples, the weightaverage fiber lengths of the reinforcing fibers were all less than 1 mmand the good physical properties were not obtained.

                  TABLE 10                                                        ______________________________________                                                                               Comp.                                             Ex. 17                                                                              Ex. 18  Ex. 19  Ex. 20                                                                              Ex. 21                                 ______________________________________                                        Fiber content (wt %)                                                                       1       3       6     18    6                                    Rod                                                                           Lw (mm)      6.0     5.2     4.6   4.5   0.6                                  Lw/Ln        1.3     1.4     1.5   1.8   0.6                                  Pellet                                                                        Lw (mm)      2.6     2.3     2.1   2.1   0.6                                  Lw/Ln)       1.4     1.4     1.5   1.9   1.6                                  Flexural modulus (MPa)                                                                     2950    3850    5080  10450 3870                                 Flexural strength (MPa)                                                                    102     124     155   215   101                                  Mold shrinkage (%)                                                                         1.3     0.78    0.44  0.14  0.93                                 Appearance of shaped                                                                       ◯                                                                         ◯                                                                         ◯                                                                       ◯                                                                       Δ                              article                                                                       ______________________________________                                    

Examples 21 to 24

Use was made of the same type of extruder as in Example 1 and, insteadof a sheet die, the die 5 shown in Table 12. Further, plates wereattached between the front end of the screw and the die 26. Polyethyleneterephthalate pellets (relative viscosity of 1.35) were supplied to theplastic feed port, that is, the first feed port 39, by a screw pelletfeeder, while glass roving of a diameter of 17 μm and a weight of 2200 gper 1000 meters (made by Nippon Electric Glass Co.) was continuouslyintroduced from the fiber feeding port, that is, the second feed port.Extrusion was performed under conditions of a cylinder temperature of280° C. and a screw rotational speed of 200 rpm. The mixture wasstranded by the strand die, that is, the die 26, and the surfaceappearance of the strands evaluated. A good ("O") rating was given whenrising of the glass fibers from the surface of the strands could not bevisually observed, while a poor ("X") rating was given when rising ofthe glass fibers on the surface of the strands could be observed.Further, the strands were pelletized to make pellets of 10 mm length andthe weight average fiber lengths of the glass fibers in the pellets weremeasured. Furthermore, a part of the strand was melt compressed and thedispersing conditions of the reinforcing fibers in the strands. As aresult, in each Example according to the present invention, noseparation between the reinforcing fibers and the resin occurred and thefibers were uniformly dispersed in the strands. The plates used werethose shown in Table 11 attached between the front ends of the screw andthe die. The results are shown in Table 11.

                  TABLE 11                                                        ______________________________________                                                     Ex. 21                                                                              Ex. 22   Ex. 23  Ex. 24                                    ______________________________________                                        Plate          FIG. 5  FIG. 6   FIG. 7                                                                              FIG. 8                                  Plate length (mm)                                                                            20      20       20    20                                      Strand appearance                                                                            ◯                                                                         ◯                                                                          ◯                                                                       ◯                           State of dispersion of fibers                                                                ◯                                                                         ◯                                                                          ◯                                                                       ◯                           Lw (mm)        2.1     2.0      1.9   1.8                                     Lw/Ln          1.4     1.7      1.5   1.6                                     Discharge state of strand                                                                    Good    Good     Good  Good                                    ______________________________________                                         Plate length: length of plate in axial direction of screw.                    Lw: Weight average fiber length in sheet                                 

Examples 25 to 29

Use was made of the same type of extruder as in Example 1 and, insteadof a sheet die, the die 6 shown in Table 12. Polyethylene terephthalatepellets (relative viscosity of 1.35) were fed to the plastic feed port,that is, the first feed port 39, by a screw pellet feeder, while glassroving of a diameter of 17 μm and a weight of 2200 g per 1000 meters(made by Nippon Electric Glass Co.) was continuously introduced from thefiber feeding port, that is, the second feed port. Extrusion wasperformed under conditions of a cylinder temperature of 280° C. and ascrew rotational speed of 200 rpm. Strands of fiber reinforced plasticwere formed by the die. These were cut and pelletized. At that time, thelength of the glass fibers in the strands and the discharge state of thestrands were studied.

                  TABLE 12                                                        ______________________________________                                               Die 1 Die 2   Die 3   Die 4 Die 5 Die 6                                ______________________________________                                        Figure   FIG. 12 FIG. 13 FIG. 14                                                                             FIG. 15                                                                             FIG. 16                                                                             FIG. 17                            Die thickness                                                                          50      50      50    50    50    50                                 (mm)                                                                          R (mm)   6       6       8     8     6     --                                 r (mm)   2       2       2     2     2     2                                  d (mm)   12      12      12    12    12    12                                 L (mm)   0       20      20    20    20    20                                 ______________________________________                                    

The results are shown in Table 13. The weight average fiber length Lw inthe strands of Examples 25 to 29 was in the range of 2.0 to 2.5 mm.Further, the state of discharge of the strands was stable. Furthermore,a part of the strand was melt compressed and the dispersing conditionsof the reinforcing fibers in the strands. As a result, in each Exampleaccording to the present invention, no separation between thereinforcing fibers and the resin occurred and the fibers were uniformlydispersed in the strands.

                  TABLE 13                                                        ______________________________________                                                   Ex. 25                                                                              Ex. 26  Ex. 27  Ex. 28                                                                              Ex. 29                                 ______________________________________                                        Die used     Die 1   Die 2   Die 3 Die 4 Die 5                                State of dispersion of                                                                     ◯                                                                         ◯                                                                         ◯                                                                       ◯                                                                       ◯                        fibers                                                                        Lw/Ln        1.5     1.7     1.6   1.8   1.6                                  Stability of discharge of                                                                  ◯                                                                         ◯                                                                         ◯                                                                       ◯                                                                       ◯                        strands                                                                       ______________________________________                                    

As clear from the above explanation and the examples, in the presentinvention, it was discovered that by controlling the degree of combingand dispersing the reinforcing fibers uniformly and by using a kneadingaction to achieve a specific distribution of fiber lengths while keepingthe weight average fiber length long, it is possible to obtain a fiberreinforced thermoplastic resin structure superior in fluidity,mechanical properties, and surface smoothness and that, further, byhaving the continuous roving wound around the screw and by theprocessing applied to the screw outer circumference and/or the cylinderinner surface, it is possible to create a comb action on the continuousroving and control the degree of combing and fiber length of thereinforcing fibers. By this, it is possible to obtain a fiber reinforcedthermoplastic resin structure with a high productivity, good fluidity atthe time of molding, and superior mechanical properties never beforeable to be obtained. The invention is therefore extremely valuable fromthe industrially viewpoints.

We claim:
 1. A fiber reinforced thermoplastic resin structure comprisingpellets obtained by cutting a sheet shaped or rod shaped fiberreinforced thermoplastic resin structure comprising a thermoplasticresin and reinforcing fibers, having a ratio (Lw/Ln) of the numberaverage fiber length (Ln) to the weight average fiber length (Lw) of theuniformly dispersed reinforcing fibers of 1.1 to 5, and having a weightaverage fiber length of 1.0 mm to 200 mm.
 2. A fiber reinforcedthermoplastic resin structure as claimed in claim 1, wherein pelletlength is not more than 1/2 of the weight average fiber length of thereinforcing fibers in the fiber reinforced thermoplastic resin structurebefore cutting and in that the weight average fiber length in thepellets is not more than 0.9 times the pellet length.
 3. A fiberreinforced thermoplastic resin structure as claimed in claim 1, whereinthe fiber reinforced thermoplastic resin structure is pellets of fiberreinforced thermoplastic resin, the ratio (Lw/Ln) of the number averagefiber length (Ln) to the weight average fiber length (Lw) of thereinforcing fibers in the pellets is 1.2 to 3.5, the weight averagefiber length is 1.0 mm to 15 mm, and the reinforcing fibers in bundlesof 10 or more constitute not more than 60% of all the reinforcing fibersobserved in a cross-section of the pellets.
 4. A fiber reinforcedthermoplastic resin structure as claimed in claim 3, wherein the pelletlength is 2 mm to 50 mm.
 5. A fiber reinforced thermoplastic resinstructure as claimed in claim 3, wherein the weight average fiber lengthis 2.0 mm to 5.0 mm.
 6. A fiber reinforced thermoplastic resin structureas claimed in claim 3, wherein the reinforcing fibers in bundles of 10or more constitute not more than 30% of all the reinforcing fibersobserved in a cross-section of the pellets.